Rotatory Steam- Engine. 41 



arranged that water, steam, air, or the gaseous productions of 

 gunpowder, shall rush out of a chamber through the arms of 

 a revolving wheel, the openings of escape being properly di- 

 rected, the recoil will urge round the wheel, and we shall liave 

 a revolving engine of Simple Emission. By availing himself of 

 this principle, the Machinist of Alexandria produced an efficient 

 engine, merely by heating a vessel containing water and air, 

 and allowing the vapour to rush from two opposite orifices at 

 the end of two arms proceeding from a sphere which the emis- 

 sion was employed to move. 



Instead of using the principle of recoil, the force of steam 

 issuing with violence as we see it from the mouth of a kettle or 

 boiler, may be directed upon the vanes of a wheel, so as to blow 

 them round ; and thus we have a second variety in the manner 

 of converting the simple issue of steam into a moving power. 

 This second species of the rotatory steam-engine of simple emis- 

 sion was invented by Branca in 1629. 



Since that time the engines of this class have been frequently 

 re-invented and slightly modified. 



Inventors of Rotatory Steam-Engines of the First Class. See PI. I. 



Figs. 1-8. 



1. Hero of Alexandria, B. C. 130. 5. Kempel, . A. D. 1785. 



2. Branca, . A. D. 1629. 6. James SadJer, ... 179I. 



3. Kircher, . ... 1643. ?. Richard Trevithie, ... 1813. 



4. Daslesme, . ... 1699. 8. Alexander Craig, ... 1834. 



The theory of machines of simple emission has been frequent- 

 ly and fully investigated, and the result is, that there is no pos- 

 sibility of obtaining, by simple emission, more than one-half of 

 the whole power of the steam, so as to make it available to use- 

 ful mechanical effect. The other half is wasted in giving off' 

 its impulsion to the air, or is expended in a current equally 

 unavailing. 



Practical experience corroborates the predictions of theory. 

 Smeaton and Pelletan made the machines of simple issue the 

 subject of careful experiment, and found that 3 parts out of 

 11, 8 parts out of 27, and 2 parts out of 5, are the highest 

 measures of practical effect that it has been found practicable 

 to attain, and by not possible improvement can more than one- 

 half of the whole power be turned to a useful effect. 



